Communication devices such as User Equipments (UEs) are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two UEs, between a UE and a regular telephone and/or between a UE and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
UEs may further be referred to as wireless terminals, wireless device, mobile terminals and/or mobile stations, mobile telephones, cellular telephones, laptops, tablet computers or surf plates with wireless capability, just to mention some further examples. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another user equipment or a server. The UE may also be a machine to machine communication device that serves as a data communication modem or is built in to equipment communicating data with server without human interaction.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node. A cell is the geographical area where radio coverage is provided by the access node.
The access node may further control several transmission points, e.g. having Remote Radio Units (RRUs). A cell can thus comprise one or more access nodes each controlling one or more transmission/reception points. A transmission point, also referred to as a transmission/reception point, is an entity that transmits and/or receives radio signals. The entity has a position in space, e.g. an antenna. An access node, also referred to as a network node, is an entity that controls one or more transmission points. The access node may e.g. be a base station such as a Radio Base Station (RBS), enhanced Node B (eNB), eNodeB, NodeB, B node, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, micro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size.
Further, each access node may support one or several communication technologies. The access nodes communicate over the air interface operating on radio frequencies with the UEs within range of the access node. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the UE to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
Selected IP Traffic Offload (SIPTO) at a Local Network, SIPTO@LN, with a stand-alone gateway is introduced in 3GPP TS 36.300 v. 11.9.0. Such an architecture enables routing of IP traffic from a User Equipment (UE) through a stand-alone Local GateWay (L-GW) without the need to go through the backhaul into a core network and back. The backhaul comprises intermediate links between a core network and network nodes in the cellular communications network.
The stand-alone gateway has local connectivity to a set of network nodes, such as an eNB and/or a HeNB. Such a network is also known as a Local Home Network (LHN). The LHN is identified by an LHN Identity (ID) signaled to the core network over an S1 interface. The S1 interface allows data transfer between the core network node and the network nodes. Knowing the LHN ID, a core network node, such as an MME, can allocate and relocate the S-GW to the most appropriate L-GW according to the UE location and the UE subscription. SIPTO may be applicable to both (e)NBs and H(e)NBs. If the SIPTO traffic offload is performed at the Local Network (LN), it is defined as SIPTO@LN.
Current SIPTO@LN does not support mobility of the UE between cells. The SIPTO@LN data connection is torn down on handover unless the LHN ID of the target network node, such as a target eNB, is the same as that of the source network node, in which case they are both connected to the same L-GW. For this reason, the core network node can also signal to the network node a relocation of gateway independently from mobility events, as disclosed in 3GPP TS 23.401 v. 12.1.0, Section 5.10.4. How to introduce this functionality in the S1AP protocol is currently being discussed by 3GPP RAN3.
When a UE moves in or out of a LHN, it may also be necessary for the MME to modify the Quality of Service (QoS) of the traffic flows Enhanced Radio Access Bearers (E-RABs). This can for example be due to the fact that the stand-alone L-GW has a different backhaul than the packet gateways in the core network and it is therefore able to provide a different, possibly even better, QoS to the UE. Currently such a modification of QoS parameters for one or more E-RABs is signaled using an S1AP E-RAB Modify procedure. S1AP is the signaling service between the RAN and the core network and fulfills the S1 Interface functions, such functions may for instance be E-RAB management functions, mobility functions for the UE, error reporting and status transfer.
A problem arises from the fact that in the current S1AP protocol, the QoS parameters are mandatory in the initiating message for the E-RAB Modify procedure, i.e. they are always comprised in an E-RAB MODIFY REQUEST message sent from the core network node to the network node.
The parameters contained within the message are also referred to as Information Elements (IEs). One of the IEs sent to modify the QoS parameters is the Non Access Stratum—Packet Data Unit (NAS-PDU) IE, which is the first packet of data to which the new parameters must be applied. Due to how the protocol is constructed, even if the message is extended with new IEs, the existing mandatory IEs are always interpreted by the receiving node. Hence a resending of a dummy or empty NAS-PDU IE if the whole message only contains e.g. a S-GW relocation, is likely to cause PDU counter mismatches and/or wrong data in the traffic flow at the receiving node. This also puts the burden on the core network node to re-send the existing, unchanged, QoS parameters for the E-RAB being relocated.
Another solution would be to introduce a new S1AP Procedure for S-GW relocation. This however has a bigger impact on the current protocol, and does not solve the issue. The core network node, such as an MME, would need to initiate two separate procedures toward the eNB, one to relocate the S-GW and another to change the QoS of the bearers. This leads to increased processing times as well as an increased load on the network.
A further solution would be to ignore the QoS parameters when the E-RAB MODIFY REQUEST message carries an S-GW relocation. This solves the problem above, but it would still require two separate procedure instances to relocate the S-GW and to modify the QoS.